In British books, the time is always given as something along the lines of "twenty-five minutes to six", which causes me to have to imagine a clock face at 6:00 and then push the minute hand back to the 7 mark. I would automatically say "five thirty five" instead. Even "half past six" sounds a bit archaic to me. Other than citing timetable/schedule entries, do our British friends say "five thirty five" in conversation? Or does that sound ... I dunno ... wonky there? Is this a generational thing (although I'm an old goat myself)?

I suspect it's largely a matter of whether or not you grew up with analog clocks or digital. If you're used to digital clocks, it's quite natural to give the exact time. With analog clocks - ones with a clock face - it's rather more natural to round off based on the position of the hands. At 5:45, the minute hand is on the left side, and it therefore closer to the next hour than the last one.